1. Field of the Invention
The invention relates to a braking system for a vehicle. More particularly, the invention relates to a refinement in control of a braking device in an electronically controlled braking system.
2. Description of the Related Art
For example, in an electronically controlled braking system for a vehicle, a braking device is driven mainly by a driving force which is independent of an operating force of an operating member, and is controlled so as to generate a braking force corresponding to an operation of the operating member. Since the braking force is directly transmitted to wheels not only by the operating force of the operating member, the operation feeling of the operating member is one of the important characteristics. A typical hydraulic braking system has a configuration, for example, for detecting an operation state of a brake pedal, which is an operating member, and for controlling a hydraulic pressure of a wheel cylinder, to which a brake pad is pressed, based on the detected operation state of the brake pedal. The operation of the brake pedal can be classified into the brake pedal depressing operation (hereinafter, referred to as the “depressing operation”) for increasing the braking force, and the brake pedal releasing operation (hereinafter, referred to as the “releasing operation”) for decreasing the braking force. It is desirable that these two types of operations are performed with the same operating feeling in the relationship with the braking force. However, due to causes such as mechanical resistance of various devices constituting the braking system, the braking force may not decrease as much as intended by a driver, or the braking force may decrease more than intended by the driver when the releasing operation of the brake pedal is performed. These are hysteresis phenomena which occur according to the configuration of the braking system, and which have a profound effect on the operating feeling of the braking system.
Japanese Patent Laid-Open Publication No. 2001-239925 and Japanese Patent Laid-Open Publication No. 2001-206208 disclose art for improving the operating feeling of the braking system by intentionally providing hysteresis in the relationship between the brake operation and the braking force. However, the operating feeling is not always improved by generating the hysteresis. On the contrary, there are many cases that the operating feeling is improved by eliminating the hysteresis that is actually generated.